In the related art, as a method of processing the surface of a semiconductor device, an apparatus that etches the semiconductor device with plasma is known. Herein, the related art will be described by using as an example a plasma etching apparatus of an electron cyclotron resonance (ECR, hereinafter, abbreviated as ECR) type.
In the ECR type, plasma is generated by a microwave in a vacuum chamber to which a magnetic field is applied from the outside. Electrons cyclotron-move by the magnetic field, and this frequency and a frequency of the microwave are resonated to efficiently generate plasma. In order to accelerate ions incident on the semiconductor device, radio frequency power is applied to a sample as an approximate sine wave in a continuous waveform. Herein, the radio frequency power applied to the sample is hereinafter referred to as a radio frequency bias.
Further, as gas which becomes plasma, halogen gas such as chlorine or fluorine has been widely used. An etched material reacts with radicals or ions generated by plasma, and thus etching is performed. A reaction product produced by etching causes reattachment to a pattern and an etching profile is a taper profile. Therefore, controlling the reaction product produced in etching becomes important in order to achieve high-precision of etching processing.
In order to decrease the concentration of the reaction product, a method of shortening a residence time of the reaction product is used. In the case where a residence time of gas in a plasma processing chamber is set as τ, τ has a relationship of τ=PV/Q when P is set as processing pressure, V is set as the volume of the plasma processing chamber, and Q is set as a gas flow rate, and in a device configuration, limitations of P, V, and Q are determined.
The residence time of the reaction product which becomes gas may be shortened by decreasing the processing pressure or increasing the gas flow rate from the above relationship, but the increasing the gas flow rate and the decreasing the processing pressure have a trade-off relationship with each other, which are difficult to be enhanced.
Further, Japanese Patent Application Laid-Open Publication No. Hei8(1996)-250479 discloses time-modulation of plasma or radio frequency bias as a method of controlling the reaction product and increasing etching processing precision. In addition, Japanese Patent Application Laid-open Publication No. 2001-85395 discloses a method of controlling a time-modulated radio frequency bias to control ion energy with high precision by dividing the radio frequency bias into two or more.